Hydro-geochemical evolution of groundwater in the central Yangtze River Basin, China

Understanding the characteristics of groundwater hydro-chemical evolution is significant for better utilization and exploitation. In this study, principal component analysis, hydro-geochemical modeling and auxiliary chemical method were used to identify the hydro-chemical evolution in the groundwater of the central Yangtze River Basin. 17.02% of the groundwater samples had TH concentrations above the China national guideline. The relationship between the concentrations of Ca2+ + Mg2+ and HCO3- in phreatic groundwater and confined groundwater indicated that they may originate from the dissolution of the same carbonate minerals (such as dolomite and calcite minerals). Values of delta O-18 and delta H-2 in phreatic water (PGW) and confined water (CGW) suggested similar evolution process of the two aquifers. delta O-18 and delta D in the mainstream of the Yangtze River presented an obvious enrichment trend along the flow direction. Principal component analysis indicated that the groundwater chemistry was mainly controlled by the anthropogenic activities and geological background. The groundwater evolution process of R2 and R3 appeared to be more similar. However, R3 was probably less affected by anthropogenic activities. The calculation results of mineral saturation index showed that calcite and dolomite were supersaturated in 96% of the groundwater at the area between the Yangtze River and Han River. This work not only strengthens the understanding of groundwater evolution in this area, but also provides a reference for groundwater analysis in other similar areas.